Sulfur steam drive



March 11, 1969 c, E, HOTTMAN ET AL 3,432,205

SULFUR STEAM DRIVE Filed Dec. 8, 1966 INVENTORS:

CLARENCE E. HOTTMAN PIETER VAN MEURS 111M 1 @vglm THEIR AGENT UnitedStates Patent 3,432,205 SULFUR STEAM DRIVE Clarence E. Hottman andPieter Van Meurs, Houston,

Tex., assignors to Shell Oil Company, New York, N.Y.,

a corporation of Delaware Filed Dec. 8, 1966, Ser. No. 600,176

US. Cl. 299-4 Int. Cl. EZlc 41/14, 43/00; E21b 43/24 4 Claims ABSTRACTOF THE DISCLOSURE This invention relates to mining sulfur. Moreparticularly, it relates to mining sulfur by circulating hot fluidthrough a sulfur deposit and recovering sulfur that is melted andentrained by the circulated fluid.

For many years sulfur has been mined by the Frasch process. In theFrasch process, hot water is injected into an upper portion of thesulfur deposit and molten sulfur is produced from a lower portion.Particularly in respect to olfshore locations, the operating costs tendto be disadvantageously high due to a need for purifying and heating arelatively large volume of hot water. The volume of the hot water mustfill all of the space that was previously occupied by sulfur. A morerecently proposed process utilizes at least two horizontally spacedwells and injects a hot gas, e.g., the gas produced by heating fluidrecovered from a petroleum reservoir, along with the hot water. Thisminimizes the amount of water that is required, but it requires both thefortuitous location of a petroleum reservoir and the compression andinjection of a large amount of hot gas. The amount of gas is largebecause it is used as an expanding gas cap that displaces the hot waterand molten sulfur in a downward direction, so that the sulfur deposit isprogressively depleted from the highest to the lowest levels within thedeposit.

In accordance with the present invention, at least two Wells are openedinto the lower portion of a sulfur deposit. Fluid communication betweenthe wells is established along a path that extends through the lowerportion of the sulfur deposit. This is preferably accomplished by afluid circulation in which a fluid having a temperature below themelting point of the sulfur and a density at least equaling that ofwater is forced to flow from one well to the other along a generallyhorizontal path through the sulfur deposit. An aqueous liquid is heated,softened and flowed between the wells at rates that are adjusted tomaintain a substantially constant temperature along the path of fluidcommunication between the wells. The temperature of the circultaingliquid is increased to between 250 to 350 F. At this temperature thesulfur will soften and become a mobile liquid. Preferably, thecirculating aqueous liquid is converted to circulating steam. Sulfur isentrained in the circulating hot aqueous fluid and is recovered byseparating it from sulfur-containing aqueous fluid that flows into aproduction well.

In completing the wells into a sulfur deposit, in order to operate thepresent process, conventional procedures and equipment can be utilized.It is generally preferable to use a relatively high ratio of productionwells to injection wells. Thermal insulation can advantageously beapplied to the injection and production tubing strings that areinstalled in the wells.

While establishing a fluid communication between a pair of wells inaccordance with the present process, although substantially any fluidhaving the specified temperature and density can be circulated betweenthe wells, it is generally preferable to circulate an aqueous liquid atthe ambient surface temperature. During such a circulation of relativelycold fluid, the injected fluid and any connate water that is present aresubstantially the only mobile fluids in the sulfur deposit. When, forexample, a cold aqueous liquid is injected at a depth within the lowerportion of the deposit while fluid is produced from another point at thesame depth, the injected liquid displaces any connate water that ispresent and flow is soon established along a substantially horizontalpath that extends through the lower portion of the deposit alongsubstantially the shortest distance between the points at which fluid isinjected and produced. In a preferred procedure, the permeability ofsuch a substantially horizontal path between the Wells is increased tothe extent required to provide a channel capable of conveying aqueousliquid through the lower portion of the deposit at the rate exceedingone-tenth barrel per minute. Although some sulfur deposits arerelatively permeable earth formations, it is often desirable that thenatural permeability be improved by fracturing, acidizing, or the liketechniques for increasing the permeability of an earth formation.

After the above type of fluid circulation has been established through apath of fluid communication between a pair of wells, an aqueous liquidis heated, softened and flowed between the wells at rates that areadjusted to maintain a substantially uniform temperature along the pathbetween the Wells. During this operation, the fluid flow rate preferablyexceeds one-tenth barrel per minute. The aqueous liquid may be initiallypumped into the injection well at about the ambient surface temperatureand then heated at a rate that is controlled in the manner describedbelow. At the outset, the aqueous liquid can be any pure, brackish orbriny water that is non-scaling at the reservoir temperature. However,as the temperature of the injected aqueous liquid is increased, theliquid should be softened to the increasing extent required in order toprovide a water that is non-scaling at the temperature to which it isbeing heated.

The rate at which the water is heated to temperatures that exceed thereservoir temperature is controlled to cause a substantially uniformheating up of the flow path between wells. This is preferablyaccomplished by measuring temperature properties of the fluids beinginjected and produced and adjusting the heating rate so that, at aselected flow rate, the measured values are indicative of the existenceof a temperature gradient of less than about 1 F. per foot along thepath between the wells. The temperature property measurements canutilize conventional methods and equipment. Such measurements can bemade at the downhole locations at which the fluids leave an injectionwell and enter a production well, or can be made at surface locationsand corrected for the tempera ture changes that occur during the flowsthrough the well conduits.

Such a substantially uniform heating up of the flow path between thewells is continued until the circulating fluid has a temperature betweenabout 250 and 350 F. at which the sulfur in the deposit is a mobileliquid. The aqueous liquid which is circulated at such a temperaturemelts sulfur in and adjacent to the flow path and the liquid sulfurbecomes entrained in the stream of hot liquid or is displaced toward theproduction well by the drag forces of the stream. The resultingextraction of sulfur converts the flow path to a channel ofsulfur-depleted earth formation. The channel of sulfur-depleted earthformation has a permeability that is materially greater than that of theundepleted sulfur deposit.

In the present process, the fluid that enters the production well isprimarily a mixture of hot water and liquid sulfur. This fluid ispreferably produced from the bottom of the well at a rate that maintainsa relatively low pressure near the bottom of the well. Such a bottomhole pressure can advantageously be about the pressure of saturatedsteam at a temperature at which the sulfur is a liquid, e.g., about 50p.s.i.g., where the sulfur is liquid at about 300 F. The fluid thatenters the production well may be produced by conveying it to thesurface by means of conventional devices or techniques such as pumping,gas lifting, or the like.

The produced fluid is preferably maintained at a temperature exceedingthe melting point of the sulfur until the fluid has reached a surfacelocation. At a surface location the sulfur may be recovered byseparating it from the other components of the fluid by means ofconventional procedures. For example, sulfur can be recovered by flowingthe produced fluid into open containers from which the aqueouscomponents are allowed to overflow and/ or evaporate to leave a depositof solidified sulfur.

In the operation of the present process, a sulfur deposit is depletedprogressively from the bottom to the top as sulfur is melted andextracted by the hot aqueous fluid that is circulated between the wells.This extraction leaves a channel of preferential permeability thatexpands vertically until it encompasses substantially the entirethickness of the sulfur deposit. Such a vertical expansion isfacilitated by the gravity segregation of the components of the fluid inthe channel. The molten sulfur, which is denser and more viscous thanthe aqueous fluid, tends to move down while the hottest and lightestportions of the aqueous fluid are moving up and over the sulfur andcooler portions of water. Such an upward migration of the hottestcomponent (preferably steam) increases the tendency for sulfur to beextracted from the roof of the channel, and causes the channel roof tomove up through the sulfur deposit until the movement is stopped bycontact with an overlying earth formation. In the present process, gascompression costs are minimized. If any gas is used, it is used merelyto gas-lift the sulfur-containing aqueous fluid from the bottoms of theproduction wells.

In conducting the present process, after the temperature within the flowpath between the wells equals the temperature of steam at the injectionpressure required to maintain an adequate rate of flow, the hot aqueousfluid that is circulated is preferably injected in the form of lowquality steam, dry steam, or super-heated steam. In offshore locationsthe water that is heated and circulated or converted to steam cancomprise sea water. The low quality steam that is used canadvantageously comprise a steam of the type produced by the process ofUS. Patent 3,193,009. Where steam is used the water consumption is lowrelative to the amount required where the sulfur is extracted by hotwater. The amount of water required to produce suflicient steam to fillthe space that was previously occupied by sulfur is much less than theamount of water that is required to fill the same space.

The drawing illustrates equipment which is suitable for practicing apreferred embodiment of the present invention. As shown, a sulfurdeposit is located between a pair of non-productive earth formationssuch as a cap rock-11 and a base rock 12. The sulfur deposit ispenetrated by an injection well 13 containing perforations 20 and aproduction well 14 containing perforations 19. The wells are opened intofluid communication with the lower portion of the sulfur deposit.

The injection well 13 contains a tubing string 15 containingperforations 21 which has a lower portion that extends into fluidcommunication with a hot geopressured aquifer 16 and is provided withvalve means 17 for controlling the flow of fluid from the aquifer. As isdescribed in US. Patent 3,258,069, such a geopressured aquifer canadvantageously be utilized as a source of hot water and/ or steam. In apreferred procedure for operating the present invention, water from theaquifer is expanded to form steam that supplements or supplants steamwhich is supplied to the tubing string 15 from a surface-located,water-heatin g device, not shown.

In using the illustrated equipment to initiate the operation of thepresent process, a relatively cool fluid, preferably an aqueous liquidthat it non-scaling at the temperature of the sulfur deposit, isinjected through well 13 with valve 17 closed and fluid is producedthrough well 14. If the natural permeability of deposit 10 is low, forexample, if it is difficult to inject fluid into the sulfur deposit at arate exceeding about one-tenth barrel per minute, it may be desirable tofracture and/or acidize the deposit. When fluid is injected and producedthrough the respective injection and production wells and the volumes offluid being injected and prouced involve the production, through a wellsuch as 14, of an appropriate proportion of the input, through a wellsuch as 13, a path of preferred fluid communication, such as path 18,has been established between the wells.

When such a path of preferred flow between the wells has beenestablished, an aqueous liquid is circulated through the path byinjecting it through well 13 with valve 17 closed and producing itthrough well 14. The circulating aqueous liquid is treated to provideincreasingly hot liquid that is non-scaling at increasingly hightemperatures and is circulated and heated at rates that are correlatedto maintain a substantially constant temperature along the flow path 18.The correlation of the heating and circulating rates is preferablyaccomplished by measuring the difference between the temperature offluid flowing through the wells 13 and 14 and adjusting the heating rateas required to maintain a difference that correlates with a temperaturegradient that is significantly less than 1 F. per foot while maintaininga flow rate that is significantly greater than one-tenth barrel perminute.

The controlled heating and circulating of the aqueous liquid iscontinued until the temperature of the circulating liquid has attained atemperature at which the sulfur in the deposit melts and becomes amobile liquid. At this time, the circulating fluid is converted from aliquid to a steam, which may be a low quality steam, i.e., steam mixedwith liquid, a dry steam, or a super-heated steam.

In a preferred procedure, the heating and circulating is accomplished bysoftening and heating sea water by flowing it through ion exchangers orother water softening means and a once-through water-heating device.Using such procedures, the circulating heated fluid is relatively slowlyconverted from liquid to steam by gradually in creasing the fluidresidence time within the heating unit without changing the pressure ortemperature of the circulating fluid. In general, the rate at which thecirculating fluid is converted from liquid to steam is preferablycontrolled by measuring the behavior with time of the temperature of thefluid that enters a production well, such as well 14, and maintaining aconversion rate that maintains a substantially constant temperature.

In a particularly suitable procedure for operating the presentinvention, the supply of the steam which is circulated through the path18 is, at least in part, switched from a surface-located water-heatingdevice to a means for flashing steam from the hot pressurized water of ageopressured aquifer, such as aquifer 16. In the illustratedarrangement, a valve means 17 is operated to expand the water from theaquifer to steam having a pressure and temperature equaling that of thesteam being circulated through the path 18. The volume of the steamderived from the aquifer is increased as that from a surface-locatedwater heater is decreased until most or all of the circulating steam isderived from the aquifer. In addition to materially reducing the cost ofgenerating the steam to be circulated into the sulfur deposit, as isindicated in U.S. Patent 3,258,069 and copending patent application Ser.No. 530,222, filed Feb. 25, 1966, the equipment and techniques forobtaining steam from such hot geopressured aquifers, provide means forrecovering byproduct hydrocarbons and/ or minerals from the watercontained in the aquifer.

We claim as our invention:

1. A sulfur mining process which comprises:

(a) opening at least two wells into the lower portion of a sulfurdeposit;

(1)) establishing preferential fluid communication between the wellsalong a path extending through the lower portion of the sulfur depositthe fluid having a temperature below the melting point of sulfur and adensity at least equal to that of water, the flow path of said fluidfrom one well to another and through the sulfur deposit beingessentially horizontal;

(c) circulating an aqueous liquid along the path beween the wells whileheating, softening, and flowing the liquid at rates adjusted to maintaina substantially constant temperature along said path;

((1) heating the circulating liquid to a temperature between about 250and 350 F. at which the sulfur in the deposit melts and becomes a mobileliquid and then converting the circulating fluid from a liquid to asteam at between 250-350 F.; and,

(e) recovering sulfur by separating it from fluid that flows into atleast one production well.

2. The process of claim 1, wherein (a) aqueous liquid is circulatedalong the path between the wells at a rate exceeding one-tenth barrelper minute; and,

(b) the circulating liquid is heated at a rate adjusted to maintain atemperature gradient of less than 1 F. per foot along the path betweenthe wells.

3. The process of claim 1, wherein (a) aqueous liquid is circulatedalong the path between the wells while heating the liquid by softeningsea water to the increasing extents required to provide briny water thatis non-scaling at the increasingly higher temperatures to which it isbeing heated; and,

(b) the circulating fluid is converted from a liquid to a steam byconverting the circulating hot briny water to a low quality steam inwhich the liquid phase is a briny water that is non-scaling at thetemperature of the steam.

4. The process of claim 1, wherein (a) at least one well in the vicinityof the sulfur deposit is completed into a geopressured aquifer having apressure and temperature that exceeds the pressure and temperature atwhich steam is to be circulated through the sulfur deposit and isequipped for flowing liquid from the aquifer through means for expandingit into steam having the pressure and temperature at which steam is tobe circulated through the sulfur deposit;

(b) the circulating aqueous liquid is initially converted from a liquidto a steam that is generated in a surface-located water-heating means;and,

(c) subsequently, at least a portion of the steam being circulated fromthe surface-located Water-heating means through the sulfur deposit issupplanted by steam which is obtained by expanding water from thegeopressured aquifer.

References Cited UNITED STATES PATENTS 988,995 4/1911 Frasch 299-42,808,248 10/1957 Prokop et al 299-4 2,947,690 8/1960 AxelrOd 299-6 X2,991,987 7/ 1961 Heinze 299-4 X ERNEST R. PURSER, Primary Examiner.

U.S. Cl. X.R.

